PITTSBURGH — People claiming responsibility for bomb threats made against the University of Pittsburgh, but only those since March 30, have promised to stop in return for the school withdrawing its $50,000 reward offer.

The school's student paper, The Pitt News, reported it received an e-mail Saturday signed by “The Threateners,” who promised to cease the threats in return for the reward withdrawal.

Vice Chancellor Robert Hill said Monday the school had withdrawn the reward offer but he declined further comment.

A joint task force of federal and local authorities is investigating the threats. The school said Sunday it would restrict final exams to five campus buildings with heightened security.